In an indictment unsealed Wednesday, authorities charged Ruben Eric Calle, 54, with uploading more than 600 illegal images, U.S. Attorney David L. Anderson of the Northern District of California said.

A member of the Silicon Valley Internet Crimes Against Children Task Force filed a criminal affidavit stating that some of the victims in the images were pre-pubescent, Anderson said. Federal agents found them when they raided Calle’s residence with a search warrant on July 11, 2018.

The investigation began when the National Center for Missing and Exploited Children received two CyberTips. Investigators later traced the uploading of the child pornography on a peer-to-peer service to Calle’s residence.

Authorities arrested him Wednesday, and later appeared in a federal court in Oakland before U.S. Magistrate Judge Donna M. Ryu. His next court date is scheduled for Tuesday.

Calle is employed as an electrician at a Bay Area News Group print facility in Concord. If convicted, he faces a maximum sentence of up to 20 years in prison and a $250,000 fine.